Approaches to understanding the molecular basis of fertilization have been severely hampered by a lack of knowledge of the macromolecules involved in this process. In particular, the materials surrounding the eggs of most animal organisms, termed egg investments or integuments, play essential roles in several aspects of fertilization such as sperm capacitation and the block to polyspermy. The biochemistry of the egg integuments is largely of a gross and/or elementary level, e.g., they are protein or glycoprotein in nature; their macromolecular composition is almost totally unknown. In an attempt to understand fertilization in molecular terms, it is proposed to: 1) determine the number and kinds of macromolecules in egg integuments of the South African clawed toad, Xenopus laevis; 2) elucidate the molecular structure of these macromolecules; 3) define the roles these macromolecules play in sperm capacitation and the block to polyspermy; and 4) correlate structural (chemical and physical) information from the molecular supramolecular, and cell ultrastructural levels with functional activity in sperm capacitation and the block to polyspermy to provide an integrated molecularly based understanding of these processes.